1. Field of the Invention
The present invention is related generally to implantable medical electrical leads. More specifically, the present invention is related to implantable neurological leads.
2. Prior Art
Neurostimulation is the application of electrical energy to neurological tissue to block the sensation of pain. A medical device, specifically an implanted neurostimulator generates an electrical pulse which is emitted from a connected lead that is implanted in the body.
Despite the many advances in neurostimulation, many problems still exist with the technology that have yet to be optimized. One of which is lead migration, the second being energy efficiency.
An ideal neurostimulation lead is designed to remain in position and emit electrical energy to a specific targeted nerve or array of nerves in an energy efficient manner. However the geometric constraints of the human anatomy sometimes make it difficult to stimulate the targeted neurological tissue in an energy efficient manner. The confined spaces of the spinal column add an increased element of complexity to neurological tissue stimulation. In addition, the delicate nature of the neurological tissue make lead fixation challenging.
One such neurostimulator lead is the percutaneous lead. This lead has a long lumen with a small cylindrical diameter. Discrete metal electrode bands are wrapped circumferentially around the proximal and distal regions of the cylindrical lumen of the lead.
The small cylindrical diameter and long slender length of the lead make it advantageous for implantation into a patient with minimal tissue trauma. Percutaneous leads are typically inserted through a small opening in the patient and advanced into position from outside a patient's body. However, despite their advantages of implantation, percutaneous leads are often ineffective in targeting specific neurological tissue in an energy efficient manner.
Using a neurostimulator implantable medical device, electrical signals are programmed to be emitted from selected electrode bands around the lead. Once activated, the percutaneous lead radially broadcast electrical energy all around the circumference of the electrode band. The lead indiscriminately emits electrical energy 360 degrees completely around the lead body in the hope of hitting the desired location of the neurological tissue.
This approach does not efficiently utilize the electrical energy of the medical device. A significant amount of electrical energy is transmitted in unintended directions away from the targeted neurological tissue. As a result of the indiscriminately broadcasted energy, a power burden is placed on the implanted medical device. This causes the device's power supply to be drained at a faster rate, thus requiring the device's power supply to be frequently replenished either through recharging or replacement. Percutanous leads also lack a fixation mechanism which makes them prone to movement within the body.
An alternative neurostimulation lead that has been designed to improve energy efficiency is referred to by those skilled in the art as a paddle lead. As its name implies, the paddle lead has a flat rectangular distal end resembling a paddle. The traditional paddle body is rectangular in shape with flat planar top and bottom sides. Electrical energy is emitted from an array of electrode pads which are typically embedded in one side of the paddle body.
Since paddle leads only have electrodes on one side, unlike that of percutaneous leads, the paddle lead can only emit electrical energy in a 180 degree semi-spherical arc from the paddle surface. Therefore, paddle leads are more energy efficient than percutaneous leads. However, a disadvantage to the traditional paddle lead is that they are typically designed with a top and bottom planar surface that do not conform to curved surfaces. This is not an ideal shape for focusing electrical energy to a specific location located around a cylindrical spinal column and spinal cord. Traditional paddle leads are an improvement in energy efficiency from percutaneous leads, however, more is desired in focusing the electrical energy to a specific area or point of neurological tissue.
Having a lead with a curved surface facing the spinal column improves the ability to focus electrical energy to specific neurological tissue and would allow for more uniform spacing between the paddle body at the distal end of the lead and the spinal column. Unfortunately, this shape alone without a fixation mechanism, would allow for the paddle body to rotate in the epidural space of the spinal column with little resistance. Paddle leads lack a fixation mechanism and therefore are susceptible to lead migration.
A curved wing paddle design is disclosed in U.S. Pat. Nos. 6,999,820 and 7,613,524, both to Jordan. As stated in both the '820 and '524 patents, “the wings on the outer edge of the lead serve to stabilize and immobilize the lead with respect to the targeted tissue and assist in focusing the electrical energy”.
However the winged electrode body design by Jordan is one rigid piece that lacks a fixation mechanism. Because of its rigid wing design, the paddle is free to rotate around the spinal cord with little resistance. This kind of movement could cause the paddle electrode to move further away from the target nerve and possibly result in an increase in the amount of cerebrospinal fluid (CSF) between the electrode and target nerve. CSF is a biological fluid that flows between the spinal cord and dura mater. An increase in CSF between the electrodes and targeted neurological tissue is not desired because it decreases the electrical efficiency of the system.
What is desired is a more energy efficient lead that conforms to the spinal column and incorporates a fixation mechanism for holding the lead in place to minimize rotation, movement and migration of the lead when implanted in the body.